Here's another wrinkle that may or may not be true. The limitations on the
number of times a region change can occur are part of the player software
so it may be possible that if Windows Media Player locks on Region 5, one
could possibly switch to, say, Real Player and get a fresh five. I was told
you can't just uninstall and reinstall the software to start over as
something gets written into the registry that can't be changed.

I believe that PCs are capable of playing DVDs from all regions. I would
assume the same for Macs. Have you encountered problems? The problem
may be in the NTSC/PAL/SECAM equation. I don't know if the average
videocard can understand/translate all the variations.